The present invention applies to the pH control of fluid systems utilized in various industrial applications including in the oil & gas industry. One of the typical uses for caustics is for scale removal and scale control, these are also uses targeted by the present invention.
In the oil & gas industry, hydroxides are mainly used in fluid systems to increase or maintain pH and alkalinity or neutralize acidic fluids, although there are many other applications for the invention. Some can be highly hazardous materials to handle because they are very hygroscopic and typically have a high exothermic reaction with other fluids, especially acids. Sodium hydroxide (NaOH) is soluble in water, ethanol and methanol. These solutions can cause severe, irreversible dermal/ocular burns and create noxious fumes that can cause serious damage to the respiratory system. NaOH may cause chemical conjunctivitis and corneal damage. Severe eye burns with clouding of the surface, and ensuing blindness may occur from exposure to liquid sodium hydroxide. Low concentration levels of mists or aerosols cause burning discomfort, spasmodic blinking or involuntary closing of the eyelids, redness, and tearing. At room temperature sodium hydroxide is a white crystalline, odorless (in solid form) deliquescent solid, which absorbs moisture from the air. When sodium hydroxide is dissolved in water, often a mist is formed. In a liquid form (50%) NaOH has a vapor pressure of 1.5 mmHg @ 68° F. (0.20 kPa @ 20° C.) Sodium hydroxide itself is nonflammable, but in contact with moisture it may ignite combustibles. Toxic fumes may be formed upon heating. The solid, solutions, mists, and aerosols are all corrosive.
Sodium hydroxide (widely utilized) is available commercially in a solid (sodium hydroxide is most commonly sold as flakes, prills, and cast blocks) or a liquid solution (normally a 50% strength). Typically in an oil & gas drilling application a solid bead or flake is added to a mixing barrel with water until solubilized and then added to the mud system or fluid system to increase the pH for various reasons, such as to limit the precipitation of calcium and magnesium from a hard water source, limit the incompatibility of the fluid system with formation clays/shales and reduce swelling effects. Another advantage of a sodium hydroxide is the liberation of hydrogen sulfide and carbon dioxide gases from the fluid system. Having an alternative product that is non-hazardous and environmentally responsible is advantageous due to the high level of human exposure in most applications, and the fact that drill cuttings (that have residuals of the mud system) are often spread over agricultural fields as a disposal technique.
A 50% sodium hydroxide solution is widely utilized in the bitumen extraction process with relation to oil-sands development. Most commercial mineable oil sands producers use an extraction method “Clarks Hot Water Extraction” Process developed in the 1920s. One of the major operational disadvantages of a 50% NaOH solution is that it begins to freeze at 13 degrees Celsius. It is therefore advantageous to have a product with a much lower freeze point, as low as minus −20 Celsius. As the waste fluids are intentional or unintentionally released into the environment post treatment, having a product that is environmentally responsible, non-toxic and non-hazardous to handle is highly advantageous. Volumes in excess of 200,000 gallons/day are utilized in the Canadian Oil Sands, and the environmental advantages for a product with these constituents are substantial.
Alkaline Surfactant Polymer (ASP) flood applications utilize a high pH fluid to aid in reservoir recovery. Having a product that is non-hazardous is an advantage. ASP formulation typically consists of about 0.5-1% alkali, 0.1% surfactant and 0.1% polymer. The alkaline component reacts with the acidic moieties that exist in the oil creating natural soap and also helps reduce the adsorption of the surfactant on the rock.
Borate crosslinked gel fracturing fluids utilize borate ions to crosslink the hydrated polymers and provide increased viscosity. The polymers most often used in these fluids are guar and HPG. The crosslink obtained by using borate is reversible and is triggered by altering the pH of the fluid system (increasing the pH generates the crosslink function, decreasing the pH eliminates the crosslink). The reversible characteristic of the crosslink in borate fluids helps them clean up more effectively, resulting in good regained permeability and conductivity. The invention can be utilized in this situation; having a minimal negative effect on polymer chains which is another advantage of the invention. Borate crosslinked fluids have proved to be highly effective in both low and high permeability formations.
Some of the major challenges faced in the oil & gas industry with respect to the use of conventional hydroxides include the following: high levels of corrosion on certain metals which are typically countered by the use of High Density Polyurethane (HDPE) components, intensive and expensive maintenance schedules—environment and equipment; reactions between hydroxides and various types of metals can vary greatly but with certain metals, such as aluminum, effects are substantial causing immediate damage. As caustics are utilized to control pH levels in many systems throughout the life cycle of a well, exposure to these metals can happen often resulting in substantial replacement costs. This renders typical hydroxide blends as controlled in most jurisdictions and require extensive labeling/handling and transportation procedures which can add to the end users costs. Additionally, the high toxicity levels of hydroxides render them banned in many offshore operations due to concerns over unintentional release into sensitive ocean ecosystems.
Like other highly corrosive alkalis, sodium hydroxide solutions can decompose proteins and lipids in skin, eyes or other living tissues via amide hydrolysis and ester hydrolysis, which consequently causes chemical burns and may induce permanent blindness if it contacts eye tissue. Solid alkali may also express its corrosive nature if there is water present on the skin or in the eyes. Sodium hydroxide is corrosive to several metals, like aluminum which reacts with the alkali to produce flammable hydrogen gas on contact. Having an alternative that is much less corrosive to metals and human tissue is advantageous.
The inherent environmental effects (organic sterility, poisoning of wildlife etc.) of caustics in the event of an unintended/accidental release on surface or downhole into water aquifers or sources of water are devastating which can cause significant pH increase of such and can substantially increase the toxicity and could potentially cause a mass culling of aquatic species and potential poisoning of humans/livestock and wildlife exposed to/or drinking the water. An unintended release at surface can also cause damaging fumes to be released, potentially endangering human and animal health. This is a common event at large storage sites when tanks split or leak. Typically if near the public, large areas need to be evacuated post event.
The inability for many caustics and blends of such to biodegrade naturally without irreversibly damaging the soil, results in expensive cleanup-reclamation costs for the operator should an unintended release occur. Moreover, the fumes produced by many bases are harmful to humans/animals and are highly corrosive and/or explosive potentially, transportation and storage requirements for liquid bases are restrictive and taxing in such that you must typically haul the products in tankers or intermediate bulk containers (IBC) that are rated to handle such corrosive-regulated products, creating exposure dangers for personnel having to handle them. Sodium hydroxide and its solutions, mists, and aerosols are rapidly damaging when they come in contact with the eyes, skin, and upper respiratory tract causing irritation, burns, coughing, chest pain and dyspnea. Swelling of the throat and accumulation of fluid in the lungs (shortness of breath, cyanosis, and expectoration) may occur. Ingestion of sodium hydroxide can cause severe corrosive injury to the lips, mouth, throat, esophagus, and stomach. There is no antidote to be administered to counteract the effects of sodium hydroxide. Treatment consists of supportive measures.
Price fluctuations with typical commodity caustics based on industrial output causing end users an inability to establish long term costs in their respective budgets; severe reaction with dermal/eye tissue; major PPE requirements (personal protective equipment) for handling, such as on site shower units; extremely high corrosion rates are some of the negatives to the industry standard bases utilized, such as sodium hydroxide (NaOH).
When used to control the pH levels on surface of water/fluid systems, caustics are exposed to humans and mechanical devices as well as expensive pumping equipment causing increased risk for the operator and corrosion effects that damage equipment and create hazardous hydrogen gas when they come into contact with water or aluminum. When mixed with acidic or lower pH fluids, caustics will create a large amount of thermal energy (exothermic reaction) causing potential safety concerns and equipment damage, caustics typically need to be blended with fresh water to the desired concentration requiring companies to sometimes pre-blend off-site as opposed to blending on-site, greatly thereby increasing costs associated with transportation.
Typical caustics used in a pH control situation can or will cause degradation of certain polymers/additives/systems/formations requiring further chemicals to be added to counter these potentially negative effects, many offshore areas of operations have very strict regulatory rules regarding the transportation/handling and deployment of caustics causing greatly increased liability and costs for the operator. Caustics or high pH fluids, such as caustic water can be destructive to many typical elastomers found in the oil & gas industry such as blow out preventers (BOP's)/downhole tools/packers/submersible pumps/seals, surface pumps and tank equipment etc., having to deal with high pH fluids during the back flush/disposal process is also very expensive. It is advantageous to have a high pH fluid that can be exported to production facilities through pipelines that once utilized, is typically non-hazardous greatly reducing disposal costs/fees.
Caustics perform many actions in the oil & gas industry and are considered necessary to achieve the desired production of various petroleum wells, maintain their respective systems and aid in certain functions (i.e. suppressing calcium & magnesium in hard waters). The associated dangers that come with using caustics are expansive and tasking to mitigate through controls whether they are chemically or mechanically engineered.
Eliminating or even simply reducing the negative effects of caustics while maintaining their performance level is a struggle for the industry. As the public demand for the use of cleaner/safer/greener products increases, companies are looking for alternatives that perform the required function without all or most of the drawbacks associated with the use of caustics.
U.S. Pat. No. 7,073,519 discloses a facility parts cleaning composition for the processing of (meth)acrylic acid and/or (meth)acrylic esters comprising an alkali metal hydroxide solution, a water-soluble amino acid, N,N′-methylene bisacrylamide, and azobisisobutyronitrile, and a cleaning method using the cleaning solution composition. Disclosed are compositions including 5 to 50 wt % of at least one alkali metal hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide, 0.01 to 1 wt % of a water-soluble amino acid, 0.001 to 0.05 wt % of N,N′-methylene bisacrylamide, and 0.001 to 0.05 wt % of azobisisobutyronitrile.
U.S. Pat. No. 7,902,137 discloses alkaline concentrated detergent composition for use in cleaning hard surfaces, medical instruments and other metal components (parts, tools, utensils, vessels, equipment). The description states that an important aspect of the invention is the utilization of a synergistic system of chlelants and scale inhibition components that are biodegradable. Chelation and scale inhibition are said to have a positive impact on cleaning performance of the compositions.
US Statutory Invention Registration no. H468 entitled “Alkaline hard-surface cleaners containing alkyl glycosides” discloses a cleaning composition comprising: (a) about 0.1 to 50 weight percent alkali metal hydroxide or ammonium hydroxide; (b) about 0.1 to 40 weight percent alkyl glycoside; and (c) about 10 to 95 weight percent water.
U.S. Pat. No. 6,387,864 discloses a laundry detergent composition comprising about 1 to about 75 parts by weight of at least one caustic compound, about 0.5 to about 50 parts by weight of at least one nonionic surfactant, about 1 to about 35 parts by weight of at least one primary amine compound.
U.S. Pat. No. 5,804,541 discloses a floor stripper composition is provided, having a pH-value above 9.0, and comprising a soap, water and a glycine-N,N-diacetic acid compound, which is preferably methylglycine diacetic acid (MGDA). The diacetic acid is desirably in the form of a divalent metal complex thereof. The description states that a good floor stripper performance could be obtained with this composition owing to its low foaming behaviour.
Since several operations in the oil industry expose fluids and equipment to very high temperatures (some upward of 200° C.), the caustic compositions used in these various operations need to withstand these high temperatures without losing their effectiveness. These compositions must be capable of being used in operations over a wide range of temperatures while not affecting the equipment or people it comes in contact with.
Consequently, there is still a need for compositions for use in the oil industry which can be used over a range of applications which can decrease a number of the associated dangers/issues typically associated with caustic applications to the extent that these caustic compositions are considered much safer for handling on worksites.